U.S. patent number 4,966,612 [Application Number 07/343,657] was granted by the patent office on 1990-10-30 for process for the separation of hydrocarbons.
This patent grant is currently assigned to Linde Aktiengesellschaft. Invention is credited to Heinz Bauer.
United States Patent |
4,966,612 |
Bauer |
October 30, 1990 |
Process for the separation of hydrocarbons
Abstract
In a process for the separation of hydrocarbons from a
hydrocarbon mixture which optionally contains components boiling
lower than methane, the crude gas stream is partially condensed and
separated into a gaseous fraction and a liquid fraction. The liquid
fraction is introduced into a rectification column wherein further
separation is performed. The residual gas obtained at the head of
the rectification column is partially condensed and introduced into
a scrubbing column wherein the condensed portion of the residual
gas is used as a scrubbing medium to scrub out low-boiling
components from the separated, gaseous fraction. For covering the
refrigeration requirement of this process, a portion of the
residual gas from the rectification column, prior to being fed into
the scrubbing column, is branched off and expanded for production
of refrigeration. After heat exchange with process streams to be
cooled, this portion of the residual gas stream is readmixed to the
residual gas stream of the rectification column.
Inventors: |
Bauer; Heinz (Munchen,
DE) |
Assignee: |
Linde Aktiengesellschaft
(Wiesbaden, DE)
|
Family
ID: |
6353045 |
Appl.
No.: |
07/343,657 |
Filed: |
April 27, 1989 |
Foreign Application Priority Data
|
|
|
|
|
Apr 28, 1988 [DE] |
|
|
3814294 |
|
Current U.S.
Class: |
62/622 |
Current CPC
Class: |
C10G
5/06 (20130101); F25J 3/0219 (20130101); F25J
3/0233 (20130101); F25J 3/0238 (20130101); F25J
3/0252 (20130101); F25J 2200/04 (20130101); F25J
2200/70 (20130101); F25J 2200/78 (20130101); F25J
2200/90 (20130101); F25J 2205/02 (20130101); F25J
2205/04 (20130101); F25J 2210/12 (20130101); F25J
2235/60 (20130101); F25J 2245/02 (20130101); F25J
2270/02 (20130101); F25J 2270/08 (20130101); F25J
2270/90 (20130101) |
Current International
Class: |
C10G
5/00 (20060101); C10G 5/06 (20060101); F25J
3/02 (20060101); F25J 003/02 () |
Field of
Search: |
;62/11,23,24,27,28,32,36 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Capossela; Ronald C.
Attorney, Agent or Firm: Millen, White & Zelano
Claims
What is claimed is:
1. In a process for the separation of hydrocarbons from a gaseous
feedstream containing light and heavy hydrocarbons, wherein said
gaseous feedstream, under superatmospheric pressure, is cooled,
partially condensed, and separated into a liquid fraction and a
gaseous fraction; said liquid fraction is fractionated by a
rectification step into a product stream containing essentially
higher-boiling components and a residual gas containing
predominantly lower-boiling components; said gaseous fraction is
introduced into a scrubbing column wherein higher-boiling
hydrocarbons are scrubbed out of said gaseous fraction by residual
gas obtained during said rectification step, after the partial
condensation of said residual gas; and a bottom liquid fraction,
obtained in the bottom of the scrubbing column, is fed to said
rectification step; the improvement which comprises:
separating said residual gas obtained during said rectification
step, after its partial condensation and prior to being fed into a
scrubbing zone of said scrubbing column, into a residual gaseous
fraction and a residual liquid fraction;
expanding at least a portion of said residual liquid fraction for
production of refrigeration;
heating said at least a portion of said residual liquid fraction by
heat exchange with partially condensing residual gas obtained
during said rectification step; and
readmixing said at least a portion of said residual liquid fraction
with said residual gas obtained during said rectification step, and
at least a portion of the remainder of said residual liquid
fraction is fed into said scrubbing column.
2. A process according to claim 1, wherein said gaseous feedstream
further contains gaseous components which boil at a lower
temperature than methane.
3. A process according to claim 1, wherein only a portion of said
residual liquid fraction is expanded for production of
refrigeration and the remainder of said residual liquid fraction is
fed into said scrubbing column.
4. A process according to claim 1, wherein, prior to its
introduction into said scrubbing column, the pressure of said
residual gas is adjusted to the pressure of said scrubbing
column.
5. A process according to claim 4, wherein the quantitative ratio
of the amount of said residual liquid fraction which is expanded
for production of refrigeration and the amount of said residual
liquid fraction which is fed to said scrubbing column is about
0.43-2.3:1.
6. A process according to claim 1, wherein, prior to readmixing the
portion of said residual liquid fraction which has been expanded
for production of refrigeration with said residual gas obtained
from said rectification step, a pressure adjustment is performed so
that the pressure of said portion of said liquid fraction and the
pressure of said residual gas are substantially the same.
7. A process according to claim 6, wherein, prior to its
introduction into said scrubbing column, the pressure of said
residual gas is adjusted to the pressure of said scrubbing
column.
8. A process according to claim 6, wherein the quantitative ratio
of the amount of said residual liquid fraction which is expanded
for production of refrigeration and the amount of said residual
liquid fraction which is fed to said scrubbing column is about
0.43-2.3:1.
9. A process according to claim 1, wherein the quantitative ratio
of the amount of said residual liquid fraction which is expanded
for production of refrigeration and the amount of said residual
liquid fraction which is fed to said scrubbing column is about
0.43-2.3:1.
10. A process according to claim 1, wherein separation of said
residual gas after its partial condensation is conducted in a
separate phase separator.
11. A process according to claim 1, wherein separation of said gas
after its partial condensation is performed in a separation zone in
an upper portion of said scrubbing column.
12. A process according to claim 1, wherein said residual gaseous
fraction after its discharge from the separation step is expanded
and heated.
13. A process according to claim 1, wherein said residual gaseous
fraction, after being discharged from the separation step, is
delivered to a H.sub.2 purification step.
14. A process according to claim 1, wherein said residual gaseous
fraction from the separation step is combined with a gaseous stream
from said scrubbing column and the resultant mixture is heated by
heat exchange with process streams to be cooled.
15. A process according to claim 1, wherein a gaseous stream
discharged from an upper portion of said scrubbing column is at
least in part cooled and partially condensed by heat exchange with
process streams to be heated, the resultant partially condensed
gaseous stream from the scrubbing column is separated into a liquid
portion and a gaseous portion, said gaseous portion is heated by
heat exchange with process streams to be cooled, and said liquid
portion is expanded and heated by heat exchange with process
streams to be cooled.
16. A process according to claim 15, wherein said residual gaseous
fraction is expanded, combined with said liquid portion, and the
resultant mixture is heated by heat exchange with process streams
to be cooled.
17. A process according to claim 1, wherein a bottom liquid
fraction accumulating in the bottom of said scrubbing column is
divided into a first bottom liquid fraction and a second bottom
liquid fraction, said first bottom liquid fraction is expanded and
delivered directly to an upper portion of said rectification step,
and said second bottom liquid fraction is heated by heat exchange
with process streams to be cooled, expanded and delivered to said
rectification step at a point below the introduction of said first
bottom liquid fraction to said rectification step.
18. A process according to claim 1, wherein said at least a portion
of said residual liquid fraction, after being heated by heat
exchange with condensing residual gas, is expanded, compressed,
heated, compressed, and heated prior to its admixture with said
residual gas obtained from said rectification step.
19. A process according to claim 1, wherein said residual gas
stream, prior to being admixed with said at least a portion of said
residual liquid fraction, is heated by heat exchange with process
streams to be cooled.
20. A process according to claim 1, wherein said residual gas
obtained from said rectification step is heated, expanded, admixed
with said at least a portion of said residual liquid fraction, and
the resultant mixture is compressed and heated prior to partial
condensation of said residual gas.
21. A process according to claim 1, wherein said at least a portion
of said residual liquid fraction, after being heated by heat
exchange with condensing residual gas, is compressed and then
heated prior to admixture with said residual gas.
22. A process according to claim 1, wherein said product stream
from said rectification step contains essentially C.sub.2+
hydrocarbons.
23. A process according to claim 1, wherein said product stream
from said rectification step contains essentially C.sub.3+
hydrocarbons.
Description
BACKGROUND OF THE INVENTION
The invention relates to a process for the separation of
hydrocarbons from a gaseous feedstream containing light and heavy
hydrocarbons and optionally containing components boiling lower
than methane. The gaseous stream is introduced to the process under
elevated pressure, cooled, partially condensed, and separated into
a liquid and a gaseous fraction. The liquid fraction is
fractionated by rectification into a product stream containing
essentially higher-boiling components and a residual gas stream
containing predominantly lower-boiling components. The gaseous
fraction separated after the partial condensation is introduced
into a scrubbing column wherein higher-boiling hydrocarbons are
scrubbed out of the gaseous fraction using residual gas obtained
during the rectification as the scrubbing medium, after the partial
condensation of this residual gas. The liquid fraction obtained in
the bottom of the scrubbing column is fed to rectification.
Such processes serve, above all, for the removal of ethane and
propane from gaseous hydrocarbon mixtures, such as natural gas or
refinery waste gases. Also, these processes are suitable for the
separation of analogous, unsaturated hydrocarbons, such as ethylene
and propylene. Refinery waste gases contain hydrocarbons of this
type, and consequently their processing has become of interest due
to rising market prices for C.sub.3 /C.sub.4 hydrocarbon
mixtures.
U.S. Pat. No. 4,707,171 discloses a process of the kind discussed
above, wherein C.sub.2+ or C.sub.3+ hydrocarbons are separated from
a gaseous mixture. A crude gas stream is partially condensed by
countercurrent heat exchange with process streams which are to be
heated. The partially condensed crude gas stream is separated in a
separator into a liquid and a gaseous fraction. The liquid fraction
consisting essentially of higher-boiling hydrocarbon components,
C.sub.2+ or C.sub.3+, is fed to a rectification column wherein
lower-boiling components are removed therefrom. During this
rectification step, a residual gas stream is obtained at the head
of the rectification column. The residual gas stream, after its
partial condensation, is introduced into a scrubbing column wherein
higher-boiling components are scrubbed out of the gaseous fraction
discharged from the separator. The bottom fraction thus obtained in
the scrubbing column is likewise introduced into the rectification
column.
The scrubbing step serves to increase the yield of the process
since this step makes it possible to remove from the gaseous
fraction of the separator, as well as from the residual gas of the
rectifying column, C.sub.2+ or C.sub.3+ components which otherwise
are unobtainable.
The above-described method has the disadvantage that the required
process temperatures must be provided by means of a refrigeration
facility, optionally a refrigeration cascade. For this purpose, a
refrigeration-producing expansion of at least part of a residual
gas stream from the scrubbing step is performed.
If it is intended to subject the residual gas stream(s) obtained to
further processing, high pressures must be maintained. In such a
case, refrigeration is produced by circulating refrigerant media in
closed cycles. However, a disadvantage of this version of the
process is that it is relatively expensive.
SUMMARY OF THE INVENTION
An object of the invention is to provide a process of the type
discussed hereinabove wherein expensive production of refrigeration
is avoided while simultaneously retaining high pressures of the
residual gas streams.
Upon further study of the specification and appended claims,
further objects and advantages of this invention will become
apparent to those skilled in the art.
These objects are attained according to this invention by
separating the residual gas obtained during the rectification,
after the partial condensation thereof and prior to its
introduction into the scrubbing column, into a residual gaseous
fraction and a residual liquid fraction. At least a portion of the
residual liquid fraction is expanded resulting in the production of
refrigeration. This portion of the residual liquid fraction is then
heated by heat exchange with residual gas from the rectification
column, the latter undergoing partial condensation. The resultant
heated portion of the residual liquid fraction is then readmixed
with the residual gas stream from rectification while the remaining
portion, if any, of the residual liquid fraction is fed into the
scrubbing column.
By branching off a portion of the condensed residual gas stream,
employing it as a refrigerating medium, and then readmixing it with
the residual gas stream from rectification, an expensive
refrigeration cascade can be avoided and high residual gas
pressures can be maintained.
The readmixture of the portion of the liquid fraction of the
residual gas stream, utilized as the refrigerating medium, with the
gaseous head product of the rectification column, i.e., the
residual gas stream from rectification, results in the total amount
of fluid circulated being greater than the actual amount of gaseous
head product from rectification. In this manner, the refrigeration
produced from the branched-off portion of the condensed residual
gas stream can be utilized for cooling additional process
streams.
Generally, the molar ratio of the branched-off residual liquid
fraction to the residual gas stream obtained from rectification
before the point of admixture is about 1:5 to 5:1, preferably 1:2
to 2:1.
In order to maintain the pressures of the individual residual gas
streams at a high level, for example for subsequent separating
steps performed on these streams, the scrubbing column as well as
the rectification column are operated under superatmospheric
pressure.
The operating pressure range of the scrubbing column is generally
about 10 to 40 bar, preferably 20 to 30 bar. In the rectification
column, the operating pressure is generally about 8 to 35 bar,
preferably 18 to 28 bar.
In one embodiment of the invention, the pressure of the portion of
condensed residual gas fed into the scrubbing column is, for this
purpose, adjusted to the pressure of the scrubbing column.
This provision ensures that the residual gas stream obtained from
the head of the scrubbing column is at an elevated pressure, the
range of the latter extending suitably up to the crude gas
pressure. The resultant gaseous head product from the scrubbing
column can thus be passed on to further separation without any
appreciable losses.
In case of a combination of H.sub.2 /C.sub.3+ separation, the
ethane-enriched gaseous head product of the scrubbing column
contributes significantly toward attainment of an adequate
Joule-Thomson effect in the subsequently arranged H.sub.2
purification stage.
The invention moreover provides that, prior to mixing the residual
liquid fraction expanded for production of refrigeration with the
residual gas from rectification, a pressure adjustment of either or
both streams is performed. The pressure of the resultant mixture
stream is adjusted to the pressure of the scrubbing column.
Adjustment of the pressures of the two streams which form the
mixture can be performed, on the one hand, by expanding one of them
to the pressure of the other, or, on the other hand, elevating the
pressure of one of the streams to the pressure of the other.
However, in either case, adjustment of the pressure of the
resultant mixture to the pressure of the scrubbing column is
subsequently effected. This is normally done by compressing the
mixture stream since the pressure level of the scrubbing column
usually lies above that of the rectification column.
Generally, the pressure difference between the two streams, prior
to pressure adjustment, which form the mixture stream is about 5 to
34 bar, preferably 15 to 30 bar. The pressure difference between
the resultant mixture stream and that of the scrubbing column is
generally about 1 to 10 bar, preferably 2 to 5 bar.
It is furthermore suggested in accordance with this invention to
make the quantitative ratio of the portion of the liquid fraction
expanded for the production of refrigeration to the portion of the
liquid fraction introduced into the scrubbing column to be about
0.43-2.3:1, preferably 0.7 - 1.5:1.
This proportion ensures, on the one hand, a continued efficient
scrubbing action in the scrubbing column and, at the same time,
makes available an adequate amount of refrigerating medium.
The process according to the invention is especially suitable for
separation of gaseous mixtures wherein the separation procedure
involves the combination of various stages for the separation of
H.sub.2 and/or hydrocarbons, operating under high inlet pressures.
Thus, it is possible, by employing the process of the invention to,
for example, perform any desired combinations of two separating
stages, consisting of separation of C.sub.5+, C.sub.3+, C.sub.2+
and/or H.sub.2, in an especially energy-saving and efficient
way.
The process is generally suitable for the separation of gaseous
mixtures containing lower- and higher-boiling hydrocarbons,
especially separation of C.sub.2+ or C.sub.3+ hydrocarbons. Thus,
the components of the gaseous mixture to be separated can, for
example, include H.sub.2, N.sub.2, CO, CO.sub.2, H.sub.2 S,
mercaptans, CH.sub.4, C.sub.2 H.sub.6, C.sub.2 H.sub.4, C.sub.2
H.sub.2, C.sub.3 H.sub.8, C.sub.3 H.sub.6, C.sub.3 H.sub.4, and/or
C.sub.3+. The process is particularly suitable for treating gaseous
mixtures comprising H.sub.2, CH.sub.4, and C.sub.2+ or C.sub.3+
hydrocarbons.
Two liquid bottoms streams are at the bottom of the scrubbing
column. One of which is actually the liquid originating from the
internals (trays, etc.) of the scrubbing column is expanded and
then delivered to an upper portion of the rectification column and
the other of which is the liquid fraction of the feed gas stream
routed to the scrubbing column, is heated, expanded, and then
delivered to the rectification column at a point below that of the
introduction of the previously mentioned liquid bottoms stream from
scrubbing. The volumetric ratio of the liquid bottoms stream which
is delivered to an upper portion of the rectification column to the
other liquid bottoms stream which is delivered to the rectification
at a point below thereof is generally about 1:10 to 10:1,
preferably 1:3 to 3:1.
The gaseous feedstreams are generally introduced into the process
at a pressure of about 10 to 40 bar, preferably 20 to 30 bar, and
at a temperature of about 250 to 350K, preferably 280 to 320K. The
pressure of residual gaseous streams discharged from the process is
generally about 4 to 38 bar, preferably 20 to 35 bar.
Without further elaboration, it is believed that one skilled in the
art can, using the preceding description, utilize the present
invention to its fullest extent. The following preferred specific
embodiments are, therefore, to be construed as merely illustrative,
and not limitative of the remainder of the disclosure in any way
whatsoever.
In the foregoing and in the following examples, all temperatures
are set forth uncorrected in degrees Celsius and unless otherwise
indicated, all parts and percentages are by weight.
The entire texts of all applications, patents and publications
cited above, and of corresponding German priority application No. P
38 14 294.5, are hereby incorporated by reference.
BRIEF DESCRIPTION OF THE DRAWINGS
Various other objects, features and attendant advantages of the
present invention will be more fully appreciated as the same
becomes better understood when considered in conjunction with the
accompanying drawings in which like reference characters designate
the same or similar parts throughout the several views, and
wherein:
FIG. 1 illustrates an embodiment of the invention wherein
separation of partially condensed residual gas from rectification
is performed in a separate phase separator; and
FIG. 2 illustrates an embodiment of the invention wherein the
partially condensed residual gas is separated into liquid and
gaseous fractions in a separation zone in an upper portion of the
scrubbing column.
DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1:
A crude gas stream at about 260 bar and about 311 K is introduced
to the process via conduit 1, partially condensed in heat exchanger
E1 by indirect heat exchange, and separated in separator D1 into a
liquid fraction and a gaseous fraction. The liquid fraction is
withdrawn via conduit 3 and, after being heated in heat exchanger
E1, is expanded into a middle zone of the rectification column T.
The gaseous fraction is removed from separator D1 via conduit 2
and, after further cooling in heat exchanger E2, is introduced at a
temperature of about 212K and a pressure of about 25.4 bar into a
lower zone of scrubbing column R (having 5 theoretical plates)
wherein further components are removed from the gaseous fraction by
scrubbing.
At the bottom of the scrubbing column R, the thus-obtained bottom
liquid fraction is discharged via conduits 7. The liquid fraction
in conduit 7 is expanded and delivered directly into an upper zone
of rectification column T. The liquid fraction of the lower feed
stream to column R which had been kept separate from the reflux
stream inside column R, in conduit 8 is first heated in heat
exchangers E2 and E1 before being expanded and delivered directly
into a middle zone of rectification column T (having 25 theoretical
plates).
From the bottom of rectification column T, a liquid product
fraction containing essentially higher-boiling components is
withdrawn via conduit 10. By way of the tap conduit 11, a portion
of the product liquid fraction in conduit 10 is branched off,
heated in heat exchanger E3, and returned to the bottom of
rectification column T as a reboiler stream. From the head of
rectification column T a residual gas stream still containing
desirable heavy components is obtained.
By means of conduit 12, this residual gas stream at a temperature
of about 288K and a pressure of about 24.0 bar is withdrawn,
partially condensed in heat , exchangers E1 and E2, and separated
in separator D3 into a residual gaseous fraction and a residual
liquid fraction. By way of conduit 14, a portion of the residual
liquid fraction, after compression in pump P, is introduced for
scrubbing purposes into an upper zone of the scrubbing column R.
Prior to compression, a portion of the residual liquid fraction in
conduit 14 is branched off by way of tap conduit 15, subjected to
expansion for production of refrigeration, heated in heat
exchangers E2 and E1 by heat exchange with streams to be cooled
from conduits 1 (crude gas) and 12 (residual gas stream from
rectification column T) and, after compression in compressors C1
and C2 and reheating in heat exchangers E4 and E5, is readmixed
with the residual gas stream from the head of rectification column
T.
The residual gas obtained at the head of scrubbing column R,
consisting of lower-boiling components, is, after discharge via
conduit 4, at least in part subjected to partial condensation in
heat exchanger E6. Thereafter, the partially condensed residual gas
is separated in separator D2 into gaseous and liquid portions. The
gaseous portion is withdrawn via conduit 6 at a pressure of about
24.0 bar. The liquid portion is heated and discharged from the
system via conduit 5 together with the residual gaseous fraction
from removed separator D3 via conduit 13 at a pressure of about 1.2
bar. The streams in conduits 5 and 6 are product streams containing
lower-boiling components. The streams 9 of heat exchanger E1 are
auxiliary cycles for production of refrigeration.
Figure 2:
A crude gas stream at about 13.3 bar and about 311 K is conducted
via conduit I, after cooling and partial condensation by indirect
heat exchange in heat exchanger E1, to separator D1 and therein
separated into a liquid fraction and a gaseous fraction. The liquid
fraction is withdrawn via conduit 3, expanded, and, after being
heated in heat exchanger E1, is conducted into a middle zone of the
rectification column T (having about 20 theoretical plates) at a
temperature of about 200 K and a pressure of about 6.6 bar. The
gaseous fraction discharged from separator D1 is, after further
cooling in heat exchanger E2, introduced via conduit 2 into a lower
zone of the scrubbing column R (having about 4 theoretical plates)
at a temperature of about 155 K and a pressure of about 12.5 bar.
Via conduits 7 and 8, the liquid fraction obtained from the bottom
of the scrubbing column is withdrawn therefrom. The liquid fraction
in conduit 8 is expanded, heated in heat exchanger E2, and
introduced into a middle zone of the rectification column T whereas
the liquid fraction in conduit 7 is expanded directly into an upper
zone of rectification column T. The liquid product fraction
obtained in the bottom of rectification column T is removed via
conduit 10. A portion of this liquid fraction is returned, after
heating in heat exchanger E3, as a reboiler stream into the bottom
of the rectification column T. The remaining portion of the liquid
product fraction is compressed by pump P and discharged after
heating in E1.
The head gaseous product of rectification column T, withdrawn by
means of conduit 12 at a temperature of about 183 K and a pressure
of about 6.5 bar, is heated in E1, expanded, and then mixed with
ther compressed and heated stream of conduit 16. The resultant
mixture is further compressed, in conduit 17, by means of
compressor C2, and then cooled in heat exchanger E5. After cooling
and partial condensation in heat exchangers E1 and E2, the stream
of conduit 17 is expanded into a separation zone of the scrubbing
column R. The separation zone is located in an upper portion of the
scrubbing column R and segregated from the actual scrubbing zone in
a lower portion of the scrubbing column R by means of a flue plate.
A gaseous product fraction is discharged at the head of the
separation zone via conduit 4 and is withdrawn from the process,
after being heated in E2 and E1, at a temperature of 308 K and a
pressure of about 12.0 bar. The liquid fraction obtained at the
flue plate is withdrawn via conduit 16 and is introduced partially
as backflow or reflux to the upper region of the scrubbing chamber.
The remaining proportion is, after expansion and heating in E2 and
E1, compressed by compressor C1, further heated in heat exchanger
E4, and mixed with the expanded head gaseous product of the
rectification column T. The streams 9 of the heat exchanger E1 are
auxiliary cycles for production of refrigeration.
The process of this invention is illustrated below with the use of
a numerical example. The numbers 1, 4, 10, 12 and 17 refer to the
streams illustrated in FIG. 2, and listed in the column under the
numbers are the mole fractions of the components in the various
streams. The crude gas enters as stream 1.
TABLE 1 ______________________________________ Mole Fractions 1 4
10 12 17 ______________________________________ H.sub.2 0.35 0.5 --
0.01 0.01 N.sub.2 0.03 0.04 -- 0.01 0.0 CO 0.0 0.0 -- 0.0 0.0
CH.sub.4 0.31 0.44 -- 0.68 0.68 C.sub.2 0.2 0.01 0.65 0.3 0.31
C.sub.3+ 0.11 -- 0.35 -- -- Pressure (bar) 13.3 12.3 6.7 6.5 13.3
Temperature (K) 311 142 234 183 311
______________________________________
The preceding examples can be repeated with similar success by
substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention, and
without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *